1. Field of the Invention
The present invention relates to clothes drying machines and more particularly to arrangements for varying the speed of rotation of the clothes dryer drum containing the articles to be dried during the drying operation.
2. Description of the Prior Art
It is generally known that in drying clothes, optimum results can be obtained if the speed of rotation of the drying drum can be varied depending on the weight and type of clothes load being dried. In the usual situation, where only a single rotative speed is used for all clothes loads, the single speed chosen for use must of necessity be a compromise speed. The speed chosen nominally will be about midway between the optimum speed for smaller loads than that for larger loads. Light loads are dried most efficiently if the drum is rotated at a speed less than the speed utilized for heavier loads. By varying the speed of the drum rotation depending upon the clothes load to be dried there is considerable effect on drying time and efficiency of the clothes dryer.
Various ways of changing the speed of rotation of the clothes dryer drum have been utilized in the past. For instance an automatic speed adjustment for clothes dryers is disclosed in U.S. Pat. No. 3,072,386 assigned to the same assignee as the present invention. In some cases a belt shifting device is used that changes the position of the belt with respect to a varying diameter of a driving shaft such as shown in U.S. Pat. No. 3,731,550. These prior art variable speed drive mechanisms were, however, complicated and often produced excessive belt wear with attendant belt failure.
In addition to having means of changing the speed of rotation of the clothes dryer drum it is often desirable to have a means to operate the dryer without rotation of the drum. This mode of operation may be desirable for mounting an internal stationary rack for hang drying certain garments and for drying items, such as tennis shoes, etc.
It is also important in production application, to have a tolerance for belt lengths; and means, preferably automatic, must be provided for taking up the slack that may result in a belt drive system due to this tolerance. Also, with use and age, the belt tends to lengthen and it is desirable that means should be provided for automatically taking up the slack that results. Prior art has taught the use of idler roller tensioners which are usually spring loaded to effect this operation. One such application is shown in U.S. Pat. No. 3,211,015--Bochan, assigned to the same assignee as the present invention. Others are shown in U.S. Pat. Nos. 3,330,049 and 3,402,617.
There is, however, no suitable mechanism for combining the functions of taking up the belt slack where idler roller tensioners may be eliminated and varying the rotational speed of the drum.
By the present invention, these deficiencies may now be overcome in that a clothes dryer having a drum rotatable at either a high speed, a low speed, or no speed and that the means also automatically adjusts for taking up any slack that results from tolerance or tendency of the belt to lengthen.